Restoration of the Drugeon River and adjacent wetlands (northeastern France): impact on breeding birds
Résumé
The channelizing of the minor bed of the Drugeon river and the drainage of adjacent marshes were carried out from 1961 to 1973 in the hope of gaining 2000 ha of farmland. Those works led to important damage to the wetlands of the Drugeon basin, a Ramsar site since 2003, under the protection of several national and European laws since 1992. Actually, two hundred hectares only were gained and the stream length was shortened by 30% (8km). This changed the river into a rectilinear channel with subsequent erosion increasing the river bottom depth from some tens of centimetres to two meters, decreasing the fish populations and leading to the extinction of the White-footed Crayfish (Austropotamobius pallipes). From 1993 to 1997 the combination of EU directives and national and regional protection laws led to achieve a LIFE programme aiming at restoring 30km of the Drugeon river. This included re-meandering the stream over 20km and filling the drains that have been dug in marshes in order to re-elevate the water table in adjacent areas. The first works begun in 1997 upstream and ended in 2001. Based on the IPA method (IBCC, 1977), the present study aims at comparing the nesting bird community between 1998-1999 (at the very beginning of the works) and 2006-2007 (5 years after the end of the works). A total of 104 nesting bird species were contacted at least once; 74 in 1998 on 15 IPAs, 80 in 1998, 94 in 2006 an 83 in 2007 on 20 IPAs. Total species richness per IPA was multiplied by 1.3 ten years after the beginning of the works and by 1.9 considering wetland species only (FIG. 2). Remarkably, bird abundance represented by the sum of the IPA scores also increased significantly (FIG. 3). Species number increase was observed all along the river but was neatly larger downstream (FIG. 4). Twelve species show a significant population increase (p < 0.05) or possibly an increase (0.05 < p < 0.1). The Willow Warbler, the MarshWarbler, the Coot, the Reed Bunting, the Mallard, the Northern Lapwing and the Little Grebe increased; the Meadow Pipit increased only in the Coot area (p < 0,05). The Common Pochard, the Tufted Duck and the Grey Wagtail possibly increased (0.05 < p < 0,1). Only theWhinchat showed a trend to decrease (0.05 < p < 0.1). Those results are discussed and compared with other bird censuses achieved along the first 80 kilometres of 5 French rivers (Seine, Saône, Loire, Allier, Loue). A remarkably high diversity of bird species was observed along the Drugeon river. The rehabilitation of the river led to improve the ecological conditions and the population of wetland species. Some of those species showed an increase in the area rehabilitated although they are known to markedly decline at European, French, Swiss and regional scales.